Building a swim platform

[CascoBay]

I would like to build a swim platform for my 26' Larson Cabrio made from fiberglass. I toyed with the idea of a teak platform but I really feel that it will not go with the boat and upkeep will always be there. The platform will be 8' x 2.5'

So my plan is to:

-Sandwich a 1.5" foam core with 1/2" plywood to give an overall thickness of 2" +/-
-Use 4 struts to support the platform underneath.
-At the strut support locations eliminate the foam and use wood.
-Cover the platform with fiberglass cloth (type/weight/# of layers?)
-Sand/Fair/Prime/Paint
-Use Durabak to create a non-skid top section

Is my proposal a valid one? Any concerns with this type of construction?

I have never used foam as a media before- and I planned on using the "tuff-board" found at most home improvement stores (not the pink stuff).

I really appreciate any input on this, thank you.

 

[Greg Mrozinski]

Re: Building a swim platform

CB,

Doesn't sound too bad. Should be plently stiff and strong. The key thing is attaching it to the boat. You will need to through bolt the platform some how to back of the boat/transom. The attachment point of the platform will have to be beefy on the platform and well supported at the bolts. Your support struts will be okay going into wood. Keep us up to date on your progress.

 

[CascoBay]

Re: Building a swim platform

Thank you for the reply. I am not too concerned with the attachment to the boat, I plan to through bolt with 3/8" stainless hardware and use large aluminum backing plates at all locations.

I will take many photos as this progresses, I am still gathering info!

 

[Greg Mrozinski]

Re: Building a swim platform

CB,

How do you plan to through bolt the sandwich of ply-foam-ply to the back of the boat?

 

[CascoBay]

Re: Building a swim platform

I plan to use 2" aluminum angle iron to form a ledge on the transom, through bolting this to the boat. This will form a shelf for the platform to sit on, I will screw or bolt at this junction.

I plan to get 3/4" stainless or aluminum tube and make the brackets for underneath the platform, such as these:

Again, everything through bolted into the transom will have a good sized backing plate.

Anything bolted into the platform for support will have a block of wood in that area and no foam.

Thats my plan anyway!

 

[CascoBay]

Re: Building a swim platform

The more I think about this the more I realize that I can do without the foam as it really doesn't provide any structural strength, it just builds the thickness of the platform.

What I am wondering now is what thickness ply I can use to span 24", I would like to use 1/2" due to weight issues, perhaps adding cloth over the 1/2" ply will make it a suitable surface.

To make the platform appear thicker, I can simply wrap the edges with 1/4" ply.

 

[jasoutside]

Re: Building a swim platform

Hey Casco! I've bookmarked your thread and am watching your progress! I have considered a swim platform for my rig down the road (way down the road).

Cheers!

 

[sasto]

Re: Building a swim platform

I like your idea of foam core. If she were mine I would make the whole thing in foam and FRP (fiberglass)......But.. foam in your application adds thickness.. which adds strength.

 

[Greg Mrozinski]

Re: Building a swim platform

CB,

Spanning 24" with 1/2" ply will give you a very springing platform between the supports. I suggest you stick with two pieces 1/2" ply. That should give you good rigity. Use another hiding strip of 1/4" x 2" ply around the edge to hide the bolts for the supports. I would wrap with at least two layers of 1708, fair and sand smooth and then cover with a finishing vail of thin cloth, like 4-6oz. Use aluminmum angle to mount to transom/stern. Should work out nice. Key is to mirror the shape of the stern on the platform to give a professional and snug fit.

 

[CascoBay]

Re: Building a swim platform

Thanks for all the input! I have been searching the net and created a folder with all of the various project photos others have done, which has only added to the confusion!

 

[Greg Mrozinski]

Re: Building a swim platform

Why don't you share some of your findings?

 

[CascoBay]

Re: Building a swim platform

Here are some images of others projects:

This is a trex decking platform, downside is weight:

Here is another:

And here is a commercially available platform for my boat:

 

[Greg Mrozinski]

Re: Building a swim platform

Thanks for sharing.

 

[CascoBay]

Re: Building a swim platform

Well I think I am going to go low-tech on this and simply use 3/4" ACX plywood wrapped in fiberglass cloth.

I will use 4 supports, with 3/4" ply 4" wide spanning the width (24") of the platform to provide a beam of sorts where the struts bolt on.

I will then take 1/4" plywood and wrap the perimeter of the platform to give it a finished look with some depth.

I will use some form of anti-skid- I was planning to use durabak but the cost is too much ($130 ish a gallon).

My only concern is that I will need some relief holes/slats for water to pass through, otherwise I am worried that water pressure could do some damage in rough seas or what have you. I am not sure if I should use a setup like the photo above and install a starboard insert with holes in it or what.

Someone tell me if I am crazy

 

[Greg Mrozinski]

Re: Building a swim platform

Sounds good. I hope the 3/4" ply will be stiff enough. 24'' is a long span. If you set it off the transom like the middle pictures you will not need to add any relief holes in the middle. Good luck and keep us posted. This should be good to follow.

 

[CascoBay]

Re: Building a swim platform

Well I will def. set if off the transom if it means I do not need any additional relief holes.

As far as the 3/4" being stiff enough, I assumed that when wrapped in fiberglass it would be fine?

 

[Greg Mrozinski]

Re: Building a swim platform

You would think. If you have a piece of 3/4" ply lying around try it with two pieces of wood under it. I have some and I will do the same and let you know.

 

[CascoBay]

Re: Building a swim platform

Thanks! I am actually on vacation this week in Myrtle Beach SC, so it will be a bit before I can give much of anything a try.

 

[oops!]

Re: Building a swim platform

click the link in my sig......and look at the index.....

there is a custom fiberglass one i built in there.

the mold was imperfect......but the platform is good.


imho....the wooden one with the gellcoating over it would be a good option.......build in a day.....quick ....easy and cheap....

glassed one inch ext grade would work very good.....you could router out the area for the swim steps.

 

[Greg Mrozinski]

Re: Building a swim platform

CB,

I took a piece of 3/4" ply and supported it across a 24" span. There was some flex when I stood on it. I recommend you follow your plan but go with two pieces of 1/2" ply bonded together to make a 1" piece of ply. Keep us posted on your progress.